Abstract
Pregnant rats were anaesthetized and exposed to doses of 25 to 2 x 100 r at varying times between the 13th and the 20th days of gestation, the beam being focused on the abdominal wall. The does were then allowed to give birth, and the young were killed at the age of 25 days. A quantitative histological study of the testes showed that there was a curvilinear relationship between the proportion of seminiferous tubules classified as normal and sterile and (i) the dose to which the animals had been exposed and (ii) foetal age at the time of exposure.